The present invention relates to a surface inspection method and apparatus for detecting various foreign matters on the surface of an inspected object.
A method has been heretofore known which enlarges a dynamic range, in a system in which detection light is incident on the surface of an inspected object to detect scattered light from foreign matter on the surface of an inspected object.
However, in the conventional detection system, the scattered light from the foreign matter is processed by one and the same processing system to secure the dynamic range of data. The scattered light from the foreign matter has not been utilized for the enlargement of continuous dynamic range due to the difference of detection object between data different in the processing system.
Further, a method for enlarging a dynamic range by software processing has been also known, but detection accuracy of sizes of foreign matter is poor as compared with the case where actual scattered light is captured.
Lately, with the progress of complicatedness and fineness of steps, it has been desired that smaller foreign matter and larger foreign matter can be measured simultaneously. The size of foreign matter on the surface of an inspected object to be measured includes a materially small size, and it is important to capture fine foreign matter with higher sensitivity.
It is necessary to grasp the more accurate size of foreign matter due to the necessity of analysis of foreign matter.
Further, it is necessary not only to measure only foreign matter but to grasp various information on the surface of an inspected object.
A wide dynamic range from small foreign matter to the rugged parts on the large surface has been obtained.
In the past, a detection device is sometimes arranged for the entirely different object in order to obtain various surface information.
However, the respective detection devices are not used for the object other than that of theirs, and are present merely for one function.
Further, in data obtained from the processing systems different from each other for processing the detection devices, even if the wide dynamic range can be achieved, data has been never prepared on the basis of foreign mater information from the high sensitivity side that sometimes includes saturated data. Therefore, the detection systems different from each other merely separately provide results. That is, there has not been proposed a widely continuous dynamic range that succeeded data from the high sensitivity side that sometimes contains saturated data.
An object of the present invention is to enable detection of various foreign matters on the surface of an inspected object with a wide dynamic range.
The present invention provides a surface inspection method and apparatus for detecting various foreign matters on the surface of an inspected object with a wide dynamic range, particularly, a widely continuous dynamic range.
In the past, since various data detected and processed by a plurality of detection systems which are different in magnification and sensitivity from each other have not been associated in data, such data have not been utilized for enlargement of the dynamic range.
However, the coordinate of data is measured accurately whereby coordinate data with high accuracy can be added to information of foreign matter. By making use of such coordinate data, even detection in the plurality of foreign matter detection systems different from each other, the continuity of foreign matter is judged to provide a wide dynamic range. The coordinate data processed by different processing system are associated to make use for enlargement of dynamic range.
In a preferred typical embodiment of the present invention, there comprises a light source section for emitting a first luminous flux and a second luminous flux irradiated on the surface of an inspected object; a first irradiation optical system in which the first luminous flux is irradiated on the surface of an inspected object at a first irradiation angle; a second irradiation optical system in which the second luminous flux is irradiated on the surface of an inspected object at a second irradiation angle different from the first irradiation angle; a displacement section for relatively displacing an inspected object and an irradiation luminous flux of the irradiation optical system; a light receiving optical system for receiving scattered light of the first luminous flux irradiated by the first irradiation optical system and produced from an inspection object on the surface of an inspected object and scattered light of the second luminous flux irradiated by the second irradiation optical system and produced from an inspection object on the surface of an inspected object; a first light receiving section for converting scattered light of the first luminous flux received by the light receiving optical system into a first light receiving signal; a second light receiving section for converting scattered light of the second luminous flux received by the light receiving optical system into a second light receiving signal; and a signal forming section for forming a measuring signal on the basis of the first light receiving signal and the second light receiving signal. The first light receiving section and the second light receiving section form a first light receiving signal and a second light receiving signal which are different in dynamic range from each other. The signal forming section synthesizes the first light receiving signal and the second light receiving signal which are different in sensitivity or dynamic range from each other to form a measuring signal.
By the provision of such constitution as described, the dynamic range of the surface inspection apparatus can be enlarged by using a plurality of processing systems different in object or a plurality of processing systems different in sensitivity.
Preferably, the first characteristic of the first luminous flux emitted by the light source section and the second characteristic of the second luminous flux emitted by the light source section lie in wavelength of luminous flux or polarized-light component.
Preferably, the first irradiation angle of the first irradiation optical system is set to be smaller than the second irradiation angle of the second irradiation optical system.
Further, the light receiving optical system comprises a first light receiving optical system for receiving a first scattered light in a first scattering direction irradiated by the irradiation optical system and emitted from an inspection object on the surface of an inspected object, and a second light receiving optical system for receiving a second scattered light in a second scattering direction irradiated by the irradiation optical system and emitted from an inspection object on the surface of an inspected object. The first scattered light received by the first light receiving optical system is converted into a first light receiving signal by the first light receiving section, and the second scattered light received by the second light receiving optical system is converted into a second light receiving signal by the second light receiving section. The first light receiving signal and the second light receiving signal which are different in sensitivity or dynamic range from each other are synthesized to form a measuring signal by the signal forming section. In this case, various kinds of light source sections can be employed. For example, a light source section for emitting a single luminous flux will suffice.
Preferably, the first scattering direction is made so as to form a larger angle in an irradiating direction of the luminous flux than a second scattering direction.
Preferably, the signal forming section extracts a foreign matter signal included in the first light receiving signal and a foreign matter signal included in the second light receiving signal to discriminate that the foreign matter signal included in the fixed range in the respective right receiving signals results from the same foreign matter, and preferentially makes use of a light receiving signal on the side satisfied with the fixed condition to form a measuring signal.
Preferably, the signal forming section forms, in the first light receiving signal or the second light receiving signal, foreign matter data by a coordinate when crossing a fixed level and a peak level in the range exceeding the fixed level.
Preferably, the signal forming section forms, where a peak level is saturated when a foreign matter signal is detected by a light receiving signal of high sensitivity out of the first light receiving signal and the second receiving signal, foreign matter data on the basis of the light receiving signal of low sensitivity.
This invention has the following effects.
Even where devices different in sensitivity and devices arranged for different objects are used, a wide continuous dynamic range can be achieved. For example, a device is made so as to be regarded as the same coordinate system whereby a wide continuous dynamic range in a true sense according to the sensitivity of device with the coordinate data as a key can be achieved.
According to the present invention, a device of high sensitivity and a device of low sensitivity are combined whereby a small foreign matter to a large foreign matter can be measured to enable achievement of a wide dynamic range.
Since even by devices different in sensitivity and devices arranged for different objects, a wide continuous dynamic range can be achieved, there can be constructed a system capable of obtaining a continuous sensitivity caused by a combination of expensive devices and inexpensive devices.
Further, according to the present invention, the coordinate is measured with high accuracy whereby even data of processing systems different from each other and data obtained from detection systems different in sensitivity from each other, a dynamic range can be enlarged simply by using the measuring data having those data synthesized.
Therefore, expensive devices (for example, a photomultiplier or the like) can be used for a high sensitivity element, and inexpensive devices (for example, a photodiode or the like) can be used for a low sensitivity element. The combination of various kinds of devices as described is able to cope with various defects on small foreign matter corresponding to fineness, large foreign matter, and the surface of an inspected object by one measurement.